President Barack Obama is to speak today at fundraisers in Exposition Park benefiting the Democratic National Committee and Sen. Barbara Boxer's re-election campaign.

In his first visit to Southern California since May and his third since taking office, Obama is set to arrive at Los Angeles International Airport this afternoon aboard Air Force One, then head to the California Science Center on a helicopter to speak at a reception.

Obama is also scheduled to speak at a dinner at the Natural History Museum of Los Angeles County. The visit comes on the heels of the state Democratic Party wrapping up its annual convention on Sunday in downtown Los Angeles.

Tickets for the reception range from $250 to $2,500 per person. A ticket to the dinner is $17,600 per person, a figure arrived at by combining half the maximum $30,400 contribution to a national party committee combined with the maximum $2,400 donation to a candidate.

A high-priced dinner with a president is a staple of both major political parties.

"This type of event is how campaigns make most of their money," said Dan Schnur, the director of USC's Jesse M. Unruh Institute of Politics.

"Candidates like to brag about the number of contributions they get from small donors. It's a very romantic image, but at this level of politics, the money tends to come in larger and larger chunks from wealthier and wealthier donors," he said.

To Schnur, "the only plausible alternative" to the current system "is public financing of campaigns and there is a significant number of people who believe their tax dollars should be spent on other things."

This will be the first time Obama will come to California to campaign on behalf of Boxer, who has said she expects to face her toughest campaign since first being elected to the Senate in 1992.

"Obama is appearing before these donors because Boxer is in trouble," said Joshua Trevino, communications director for the campaign of Assemblyman Chuck DeVore, one of three major candidates seeking the Republican nomination to oppose Boxer.

"Multiple polls over the past year suggest that Boxer is one of the most vulnerable incumbents on the Democratic side so that's why they're bringing out the big guns. She is very key to their agenda and as such, they're going to defend her."

Boxer campaign manager Rose Kapolczynski said "we're thrilled that President Obama will be campaigning for Senator Boxer to help her win reelection and keep fighting in the Senate to create jobs and turn the economy around."

A poll of 1,102 likely voters conducted March 9-16 by the Public Policy Institute of California found that Boxer trailed former Rep. Tom Campbell, 44 percent to 43 percent, and led former Hewlett-Packard Chief Executive Officer Carly Fiorina, 44 percent to 43 percent, and DeVore 46 percent to 40 percent.

With the margin of error of 3 percentage points, both the Boxer-Campbell and Boxer-Fiorina races are considered statistical ties.

"If the three interim elections in New Jersey, Virginia and Massachusetts are any indicator, President Obama's campaign appearance signals the beginning of Barbara Boxer's farewell tour," said James Fisfis, a spokesman for the Campbell campaign, referring to Republican victories in the New Jersey and Virginia gubernatorial elections and Massachusetts' Senate special election.

Trevino called those able to pay for tickets to attend the dinner "Barbara Boxer's base, these monied elites who don't have the same economic worries as the rest of us."

"We've always known that a lot of the big, entrenched liberal money is going to go to Boxer," Trevino told a local wire service.

"What matters here isn't really so much the money, it's the votes. The votes, as measured by opinion polls are not on Boxer's side. She can hold all the big-money fundraisers she wants. We're more interested in the big number of voters."

There was no immediate response to a request for comment from the Fiorina campaign.

Groups calling for the immediate withdrawal of all U.S. troops from and Iraq and Afghanistan plan a protest in Exposition Park in connection with Obama's visit.

"As an Iraq war veteran, I understand the importance of stopping these unjust wars," said Mike Prysner, founder of March Forward!, a veterans and active duty service members organization that opposes U.S. involvement in the wars in Iraq and Afghanistan.

"Too many civilians and soldiers are dying, too much money is going to fund death and destruction, while so many of us are hurting here at home."

Obama has pledged to end the U.S. combat mission in Iraq by Aug. 31, with Iraqi Security Forces then having full responsibility for major combat missions, and to remove all U.S. troops from Iraq by the end of 2011.

Obama announced last year that the U.S. strategy is to disrupt, dismantle and defeat al Qaeda in Pakistan and Afghanistan, and to prevent their return to either country in the future.

Obama is scheduled to leave Los Angeles Tuesday morning to return to Washington.